SHANGHAI - CHINA'S past 30 years of reforms have planted seeds that will in the coming decades produce future coastal megacities, an urban population of one billion and possibly the world's biggest economy.

What the next 30 years of reforms have in store may be unclear but experts agree that with widespread pollution problems and a tidal wave of migration set to hit China's cities, urbanisation will be the nation's biggest challenge.

'The next 30 years are going to be a critical timetable for addressing all the needs of a large population and how China manages cities,' said James Canton, author of The Extreme Future.

By 2025 China's urban population is expected to rise to 926 million from 572 million in 2005, an increase of more than the current US population, according to management consultants McKinsey and Company.

By 2030 that number will increase to a billion.

Over the next two decades China will build 20,000 to 50,000 new skyscrapers - the equivalent of 10 New York cities, according to McKinsey.

More than 170 cities will need mass transit systems by 2025 - more than twice the number in all of Europe - in what McKinsey described as the 'greatest boom in mass-transit in history'. Chinese cities will leverage their manufacturing strengths to become innovation centres for products such as nanotechnology, smart materials and state-of-the-art pharmaceuticals, Canton predicted.

They will also be home to the world's largest middle class, he said. But to accommodate more than a billion people, entirely new forms of infrastructure and security frameworks will need to be developed.

'You're going to have to say no to somebody. You will see the emergence of biometric identification; you will not be able to enter some cities,' he said.

As cities become bigger, land reclamation will leave little water between Hong Kong and the mainland, Canton forecasted.

And he said demographic, economic and ecological pressure will leave China with no choice but to try innovative solutions.

'Very few times in the history of a global civilisation will you see this ability of creating something fresh and new,' Canton said. 'They are going to do some very stunning things in terms of the next cities of the future.

Economist and urban planner Stanley Yip is already working on the next generation of Chinese cities.

He is leading British engineering consultancy Arup's work with various cities across China on experimental eco-towns as part of a drive by Beijing to develop competing sustainable solutions.

The future of Chinese architecture and design could be dictated by a new law requiring all new buildings to cut energy use by half by the end of 2010, he said.

To meet those requirements new buildings will be stripped down, flooded with natural light, super-insulated in cooler northern cities, and more open and ventilated in the south. Solar panels will become common features.

'All these devices will come in and they will start to change the look and feel of the buildings,' Mr Yip said.

China's economy is currently the world's fourth biggest and by 2025 it is expected to overtake Japan for the number two spot, according to the US National Intelligence Council.

The biggest threats facing China's communist leaders are urban challenges such as the growing gap between the rich and poor, a fraying social safety net, official corruption and environmental damage, the council said.

But barring a 'perfect storm', where several of these problems escalate dramatically at the same time, the Communist Party is likely to maintain its grip, it said in its latest forecast.

By 2038, China will likely be the world's largest economy but most incomes will still lag behind the West, said Professor Yao Shujie, head of Nottingham University's School of Contemporary Chinese Studies.

The next generation of leaders' priorities will be mending the country's social and environmental fabric, Prof Yao said.

'The last 30 years didn't do so well in terms of equality and social justice and the environment and there was slow progress in terms of political reform,' Prof Yao said. 'These are going to be the biggest challenges in the next 30 years.' -- AFP